A control of a displacement machine of this general type is known from German Patent Publication DE No. 38 38 767 C2, where at the time of each shifting change the displacement volume is adjusted in accordance with a theoretical oil requirement plus a certain leakage loss, so that the clutch of the previous gear which is to be disengaged can be disconnected as torque-free as possible. Determination of a leakage loss to be taken into consideration represents a very inaccurate compromise, because the displacement machine operates with different hydraulic transmission segments before and after the shift points of successive gear stages. The hydraulic pressure conditions and thus the leakage losses are therefore of different sizes, something which was not considered. Thus the intended disengagement of the clutch members at low torque is either never attained or only when upshifting or down-shifting, which inevitably results in damage to the clutch and the gear, and in a jerky operation.